This invention relates to a transient voltage and current suppression system for use with electrical power systems having at least one power line and one neutral or ground line.
It is desirable to eliminate, to the extent possible, transient voltages in electrical power systems since such voltages may damage electrical apparatus such as motors and household appliances connected to the power systems. In addition, such transient voltages may cause the electrical apparatus to overheat so that it operates less efficiently and thus at a greater cost to the user.
Transient voltages are produced in electrical circuits by such events as relay switching, motor commutator cycling, contact arching, and in generally any repititious on/off cycling events. Also, transient voltages may be caused by atmospheric events such as lightening and this type of transient voltage is especially destructive to electrical apparatus.
Transient voltage suppression is generally achieved with the use of various types of voltage clamping devices which are coupled either between the power lines of a system, between the power lines and a neutral or ground line, or both. When the voltage on a power line exceeds some predetermined level, the voltage clamping device becomes conductive to thereby "clamp" or maintain the voltage on the line at or below the predetermined level. In this manner, electrical apparatus connected to the power system is protected.
Because most voltage clamping devices have certain operating characteristics and limitations, if excessive current or voltage surges occur, it is possible that the clamping devices will be damaged so that they cannot perform their protective function. Typically, voltage clamping devices which have low breakdown voltage ratings cannot withstand excessive transient voltages or currents, whereas voltage clamping devices having high breakdown voltage ratings can withstand such voltages or currents. Thus, on the one hand it would appear desirable to select voltage clamping devices having high breakdown voltage ratings simply because such devices would be less likely to be damaged, but on the other hand it is desirable to "clamp" transient voltages at lower levels than can be achieved with the higher rated devices. Of course, it would be desirable to provide some type of voltage suppression arrangement which could "clamp" the voltage on power lines at some selected level without exposing the voltage clamping devices to damage from high transient voltages or currents.